When people communicate with each other over a distance, there is often uncertainty as to whether the participants hear each other. The uncertainty can be attributed to noise or other forms of impairment that are present in the transmission path between the participants. In radio communication, for example, impairments can come in the form of co-channel interference, Rayleigh fading, thermal noise, and so forth. Even in landline communications, in which a radio link is not present, impairments can still come in the form of echoes, transcoding errors, packet losses, and so forth.
The uncertainty in achieving successful communication is not specific to any one form of communication. This is evident, for example, in two-way radio communication for military, aerospace, or public service purposes, in which the participants are often forced to repeat what was heard. Additionally, in order to acknowledge and confirm the accuracy of the communication explicitly, the participants often have to use words such as “roger” to indicate that information has been received or “copy” to indicate that what was just said is understood. Even in cellular telecommunications, which comprises an adapted form of two-way radio communication, commercials and advertisements by the cellular service providers often feature themes of anxiety caused by a cell phone user not hearing someone else or of a service rep continually asking if someone else is able to hear him on his cell phone.
Not surprisingly, a lot of effort has been spent on improving the robustness of communications and ensuring each participant in a conversation that the other person is, in fact, hearing him. In a Voice over Internet Protocol context, for example, protocols such as Real-time Transport Control Protocol (RTCP) have been developed to deal with improving the robustness of communication, among other things. RTCP in particular provides out-of-band control information for a Real-time Transport Protocol (RTP) packet stream that conveys voice or other media information between endpoints. RTCP is intended to be used to transmit control packets periodically to participants in a streaming multimedia session, such as that transacted during a VoIP call. The primary function of RTCP is to provide feedback on the quality of service that is being provided for the transmitted RTP packet stream. The receiving endpoint of a packet stream can transmit RTCP packets back to the transmitting endpoint, in order to report the quality of service being experienced by the receiving endpoint.